Change in inference behaviour after JDK-8078093

[Liam Miller-Cushon]

Thanks Maurizio! For what it's worth, it looks like this only affects a
very small amount of code.

On Fri, Jan 15, 2016 at 2:25 PM, Maurizio Cimadamore <
maurizio.cimadamore at oracle.com> wrote:

> Hi Liam,
> it's likely a regression in handling of unchecked calls introduced by that
> fix.
>
> On a closer look, the problem seems to be caused by the fact that the code
> in Attr::checkMethod reuses the same Warner object (a problem that keeps
> biting us :-() - as the new code shares more state than the previous
> speculative-based implementation, the compiler ends up resetting the Warner
> when checking 'destination.get()' so that the compiler loses track of the
> fact that it had already encountered an unchecked warning during the
> applicability check of the first argument (Class <: Class<L>) -
> subsequently, the call is not flagged as unchecked, and a spurious
> inference error is then thrown.
>
> I will fix it.
>
> Filed: https://bugs.openjdk.java.net/browse/JDK-8147493
>
> Thanks
> Maurizio
>
>
> On 15/01/16 19:48, Liam Miller-Cushon wrote:
>
>> It reproduces in jdk9-dev at head, and bisects to the fix for JDK-8078093
>> [1][2]. Earlier versions of javac do not report the error. Is this a bug?
>>
>> === Test.java ===
>> abstract class Test {
>>   interface One {}
>>   interface Two<I extends One> { I get(); }
>>   interface Three<T> {}
>>   interface Four<T> {}
>>
>>   <E extends Two<?>, L extends Three<E>> Four<L> f(Class raw, E
>> destination) {
>>     return g(raw, destination.get());
>>   }
>>
>>   abstract <I extends One, E extends Two<I>, L extends Three<E>> Four<L>
>> g(
>>       Class<L> labelClass, I destinationId);
>> }
>> ===
>>
>> $ javac Test.java
>> error: incompatible types: inference variable I has incompatible bounds
>>     return g(raw, destination.get());
>>             ^
>>     equality constraints: CAP#1
>>     lower bounds: One
>>   where I,E,L are type-variables:
>>     I extends One declared in method <I,E,L>g(Class<L>,I)
>>     E extends Two<I> declared in method <I,E,L>g(Class<L>,I)
>>     L extends Three<E> declared in method <I,E,L>g(Class<L>,I)
>>   where CAP#1 is a fresh type-variable:
>>     CAP#1 extends One from capture of ?
>> 1 error
>>
>> [1] http://hg.openjdk.java.net/jdk9/dev/langtools/rev/286fc9270404
>> [2] https://bugs.openjdk.java.net/browse/JDK-8078093
>>
>
>
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